1. Field of the Invention
The present invention relates to a technique of generating a print image, that includes an image pattern or a character string to be visualized, on a printing medium under infrared light.
2. Description of the Related Art
As an anticounterfeit or authentication technique for a printed product, a printing method that uses an apparatus having a given sensitivity to the infrared range, such as an infrared camera, to allow an image which cannot be visually observed (or can be hardly visually observed) under ordinary light to be easily recognized under infrared light is available.
A typical example of the above-mentioned printing method is a method of printing an image using a color material of black (k), that is employed in general printing operations, because of its high infrared absorbance (Japanese Patent No. 3544536). An image is printed on a printing medium using black (k) having a high infrared absorbance in a latent image region, and using cyan (c), magenta (m), and yellow (y) having low infrared absorbances in a background region. The output printed product is irradiated with infrared light to identify the image using an infrared camera. This allows authentication, in which a printed product having an image that can be identified under infrared light is determined to be authentic, and a printed product having an image that cannot be identified under infrared light is determined to be counterfeit.
In generating a copy, that is, a counterfeit product of a printed product output using the above-mentioned method, it is a common practice to use a scanner and a printer. A copy generated using a scanner and a printer generally has an image that cannot be visually observed under ordinary light but can be identified by observation through an infrared camera upon irradiation with infrared light, despite its degradation in quality, compared to the original image of an authentic product. This means that a copy which has the same effect as an authentic product can be generated.